Known methods of acquiring an image of a biometric object for biometric authentication include methods using transmitted light and methods using reflected light. To acquire an image of a biological object located under the skin, such as a vein, diffused light, among the reflected light, that is reflected back after being diffused inside the hand is used. In such a case, surface reflected light that reflects at the skin becomes noise. When the surface reflected light and the diffused light are superimposed, detection of the biological object becomes difficult.
Japanese Laid-open Patent Publications Nos. 2002-112970 and 2002-200050 disclose techniques using polarized illumination. Japanese National Publications of International Patent Application Nos. 2002-501265 and 2002-514098 and Japanese Laid-open Patent Publication No. 2002-133446 disclose techniques using a plurality of lights for acquiring an image with each light. Japanese Laid-open Patent Publication No. 2001-224549 discloses a technique for acquiring a reflection image by processing an image through a low-pass filter.